Supporting a large number of devices in wireless communications

ABSTRACT

A method for receiving a backoff value at a wireless station is presented. A traffic indication map is received at the station, wherein a backoff number is implicitly assigned to the station based on a position of the station within the traffic indication map. The backoff value is determined by multiplying the backoff number by a predetermined time value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/607,354, filed Mar. 6, 2012, U.S. Provisional PatentApplication No. 61/669,274, filed Jul. 9, 2012, and U.S. ProvisionalPatent Application No. 61/696,607, filed Sep. 4, 2012, the entirecontents of which are hereby incorporated by reference as if fully setforth herein.

BACKGROUND

A wireless local area network (WLAN) in infrastructure basic service set(BSS) mode has an Access Point (AP) for the BSS and one or more stations(STAs) associated with the AP. The AP typically has access to orinterfaces with a distribution system (DS) or another type ofwired/wireless network that carries traffic in and out of the BSS.Traffic to the STAs that originates from outside the BSS arrives throughthe AP and is delivered to the STAs. Traffic originating from the STAsto destinations outside the BSS is sent to the AP to be delivered to therespective destinations. Traffic between STAs within the BSS may also besent through the AP where the source STA sends traffic to the AP and theAP delivers the traffic to the destination STA. Such traffic betweenSTAs within a BSS is really peer-to-peer traffic. Such peer-to-peertraffic may also be sent directly between the source and destinationSTAs with direct link setup (DLS) using an 802.11e DLS or an 802.11ztunneled DLS (TDLS). A WLAN in Independent BSS mode has no AP, and STAscommunicate directly with each other.

Enhanced distributed channel access (EDCA) is an extension of the basicDistributed Coordination Function (DCF) introduced in 802.11 to supportprioritized Quality of Service (QoS). The operation of EDCA in 802.11nis shown in FIG. 1.

The point coordination function (PCF) uses contention-free channelaccess, and includes the following properties: supports time-boundedservices; polling by the AP; the AP sends a polling message afterwaiting for a PCF interframe space (PIFS); if a client has nothing totransmit, it returns a null data frame; since the PIFS is smaller than aDCF interframe space (DIFS), it can lock out all asynchronous traffic;it is deterministic and fair; and it is efficient for both lowduty-cycle and heavy/bursty traffic.

The hybrid coordination function (HCF) controlled channel access (HCCA)is an enhancement of PCF. The AP can poll a STA during both a contentionperiod (CP) and a contention-free period (CFP), and may transmitmultiple frames under one poll.

The traffic indicator message (TIM)-based power saving mechanism may beused in 802.11. Basic power management modes are defined and includeAwake and Doze states. The AP is aware of the current power saving modesused by STAs it is addressing and buffers the traffic status for STAsthat are in a sleep, or Doze state. The AP notifies corresponding STAsusing the TIM/delivery traffic indication messages (DTIM) in beaconframes. The STA, which is addressed by the AP, may achieve power savingsby entering into the Doze state, and waking up to listen for beacons toreceive the TIM to check if the AP has buffered traffic for it toreceive. The STA may send a power saving (PS)-Poll control frame toretrieve buffered frames from the AP. The STAs may use a random back-offalgorithm before transmitting the PS-Poll frames if and when multipleSTAs have buffered frames waiting for reception from the AP.

An example of the TIM and DTIM operation is shown in FIG. 2. The TIM isindicated using an association identifier (AID) bitmap or a partialvirtual bitmap. The STAs that currently have buffered bufferable units(BUs) within the AP are identified in a TIM, which is included as anelement in all beacon frames generated by the AP. A STA determines thata BU is buffered for it by receiving and interpreting the TIM.

In a BSS operating under the DCF or during the CP of a BSS using thePCF, upon determining that a BU is currently buffered in the AP, a STAoperating in the PS mode transmits a short PS-Poll frame to the AP. TheAP responds with the corresponding buffered BU immediately, oracknowledges the PS-Poll and responds with the corresponding BU at alater time. If the TIM indicating the buffered BU is sent during a CFP,a CF-Pollable STA operating in the PS mode does not send a PS-Pollframe, but remains active until the buffered BU is received or the CFPends.

At every beacon interval, the AP assembles the partial virtual bitmapcontaining the buffer status per destination for STAs in the PS mode andsends the bitmap in the TIM field of the beacon frame. At every beaconinterval, the automatic power-save delivery (APSD)-capable AP assemblesthe partial virtual bitmap containing the buffer status ofnon-delivery-enabled access categories (ACs) (if there exist at leastone non-delivery-enabled AC) per destination for STAs in the PS mode andsends the bitmap in the TIM field of the beacon frame. When all ACs aredelivery-enabled, the APSD-capable AP assembles the partial virtualbitmap containing the buffer status for all ACs per destination. Ifflexible multicast service (FMS) is enabled, the AP includes the FMSdescriptor element in every beacon frame. The FMS descriptor elementindicates all FMS group addressed frames that the AP buffers.

The maximum length of an information element in the current 802.11standards is 256 bytes, which is determined by the one-byte length fieldin the element format. Consequently, this maximum Information Element(IE) size limits the number of STAs that can be supported in the TIM IE,as the TIM uses the bitmap to signal the STAs with buffered downlink(DL) BUs by mapping the STA's AIDs to the bits in the bitmap. Inaddition to the bitmap field, the TIM element also contains otherinformation fields, for example, DTIM Count, DTIM Period, and BitmapControl. Therefore, the maximum size of the bitmap field in the TIMelement is further limited to 251 bytes.

For the current maximum of 2007 AIDs, the full bitmap needs 2007 bits(251 bytes), which is the maximum size of the bitmap field in the TIM.Therefore, the current TIM with its bitmap structure cannot support morethan 2007 STAs. The length of the TIM element increases as the number ofsupported STAs increases, based on the current TIM element structure asspecified in the 802.11 standards. For example, with a maximum of 2007STAs, the worst case bitmap in the TIM element is 251 bytes. If themaximum number of STAs is increased to a larger number, for example,6000, then the worst case bitmap would be 6000/8=750 bytes. Such a largesize TIM increases the overhead of the TIM/beacon transmission andlikely takes it out of the acceptable level, particularly in systemswhere the channel bandwidth, for example, 1 MHz, 2 MHz, up to 8 MHz, issmaller than other systems.

The following provides an example of analyzing the TIM/beacon overheadin an 802.11ah system, by assuming that a typical beacon has a size of230 bytes and a transmission rate of 100 Kbps. If a typical beacon framecontains a 30-byte TIM element out of a 230-byte beacon frame, itimplies that there are 200 bytes of non-TIM content in a beacon frame.

Considering that a typical bitmap may be smaller than the worst case, itis assumed that the typical size of a TIM bitmap is one-third of theworst case, i.e., 250 bytes for 6000 STAs, which results in a 255-byteTIM element. The beacon frame would be 200+255=455 bytes, counting 200bytes of non-TIM content. If the beacon is transmitted at the rate of100 Kbps, the 455-byte beacon frame will take at least 455×8/100=36.4 msto transmit. Since the beacon interval is typically set up to be 100 ms,beacon frame overhead is 36.4%, which does not include the time used forchannel access and inter-frame spacing. For the worst case scenario inwhich the TIM size is 755 bytes, the beacon frame would be 200+755=955bytes, corresponding to a 76.40 ms transmission time, or 76.4% of a100-ms beacon interval.

The Power-Save Multi-Poll (PSMP) mechanism is introduced in 802.11n andhas the following features. It may use a single PSMP frame to schedulemultiple STAs instead of the direct QoS (+) CF-Poll used in HCCA. Thescheduling is more efficient under the scenario where the STAsperiodically transmit a small amount of data. It may reduce powerconsumption by providing an uplink (UL) and a DL schedule at the startof the PSMP phase, so that each STA may shut down their receivers untilneeded in the DL phase and transmit when scheduled during the UL phasewithout performing clear channel assessment (CCA). An example of PSMPoperation of three STAs is shown in FIG. 3.

SUMMARY

A method for receiving a backoff value at a wireless station ispresented. A traffic indication map is received at the station, whereina backoff number is implicitly assigned to the station based on aposition of the station within the traffic indication map. The backoffvalue is determined by multiplying the backoff number by a predeterminedtime value.

A wireless station includes a transceiver and a processor. Thetransceiver is configured to receive a traffic indication map, wherein abackoff number is implicitly assigned to the station based on a positionof the station within the traffic indication map. The processor is incommunication with the transceiver, and is configured to determine abackoff value for the station by multiplying the backoff number by apredetermined time value.

A method for assigning a backoff value to a wireless station ispresented. A traffic indication map is sent to the station, wherein abackoff number is implicitly assigned to the station based on a positionof the station within the traffic indication map. The backoff value isdetermined by multiplying the backoff number by a predetermined timevalue.

A method for receiving a backoff value at a wireless station ispresented. A traffic indication map is received at the station. On acondition that the traffic indication map contains a positive trafficindication for the station, a hash function with a predetermined set ofparameters is used to determine the backoff value for the station.

A wireless station includes a transceiver and a processor. Thetransceiver is configured to receive a traffic indication map. Theprocessor is in communication with the transceiver, and is configured touse a hash function with a predetermined set of parameters to determinea backoff value for the station on a condition that the trafficindication map contains a positive traffic indication for the station.

A method for assigning a backoff value to a wireless station ispresented. A traffic indication map is sent to the station. On acondition that the traffic indication map contains a positive trafficindication for the station, a hash function with a predetermined set ofparameters is used to determine the backoff value for the station.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawings,wherein:

FIG. 1 is a diagram of EDCA operation;

FIG. 2 is an example of TIM and DTIM operation;

FIG. 3 is an example of PSMP operation of three STAs;

FIG. 4A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 4B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 4A;

FIG. 4C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 4A;

FIG. 5 is an example of an AP polling a STA to send buffereddata/traffic;

FIG. 6 is a diagram of an example of a dynamic associated time unit (TU)values information element for a TIM;

FIG. 7 is a flowchart of a method for a STA to transmit packets;

FIG. 8 is a flowchart of a method for a STA to retrieve packets waitingfor it;

FIG. 9 is a diagram of a backoff information element format;

FIG. 10 is a diagram of an interval schedule information element format;

FIG. 11 is an illustration of AP/STA behavior for a controlledcontention interval;

FIG. 12 is a diagram of a registration ID (RID) format;

FIG. 13 is a diagram of a RID-based TIM element format; and

FIG. 14 is a diagram of an alternate RID-based TIM element format.

DETAILED DESCRIPTION

FIG. 4A is a diagram of an example communications system 400 in whichone or more disclosed embodiments may be implemented. The communicationssystem 400 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 400 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems400 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 4A, the communications system 400 may include wirelesstransmit/receive units (WTRUs) 402 a, 402 b, 402 c, 402 d, a radioaccess network (RAN) 404, a core network 406, a public switchedtelephone network (PSTN) 408, the Internet 410, and other networks 412,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 402 a, 402 b, 402 c, 402 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 402 a, 402 b, 402 c, 402 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 400 may also include a base station 414 a anda base station 414 b. Each of the base stations 414 a, 414 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 402 a, 402 b, 402 c, 402 d to facilitate access to one or morecommunication networks, such as the core network 406, the Internet 410,and/or the networks 412. By way of example, the base stations 414 a, 414b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 414 a, 414 b areeach depicted as a single element, it will be appreciated that the basestations 414 a, 414 b may include any number of interconnected basestations and/or network elements.

The base station 414 a may be part of the RAN 404, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 414 a and/or the base station 414 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 414 a may be divided intothree sectors. Thus, in one embodiment, the base station 414 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 414 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 414 a, 414 b may communicate with one or more of theWTRUs 402 a, 402 b, 402 c, 402 d over an air interface 416, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 416 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 400 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 414 a in the RAN 404 and the WTRUs 402 a, 402b, 402 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 416 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 414 a and the WTRUs 402 a, 402b, 402 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface416 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 414 a and the WTRUs 402 a, 402 b,402 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 414 b in FIG. 4A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 414 b and the WTRUs 402 c, 402 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 414 band the WTRUs 402 c, 402 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 414 b and the WTRUs 402 c, 402 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 4A,the base station 414 b may have a direct connection to the Internet 410.Thus, the base station 414 b may not be required to access the Internet410 via the core network 406.

The RAN 404 may be in communication with the core network 406, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 402 a, 402 b, 402 c, 402 d. For example, the core network 406may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 4A, it will be appreciatedthat the RAN 404 and/or the core network 406 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 404 or a different RAT. For example, in addition to being connectedto the RAN 404, which may be utilizing an E-UTRA radio technology, thecore network 406 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 406 may also serve as a gateway for the WTRUs 402 a,402 b, 402 c, 402 d to access the PSTN 408, the Internet 410, and/orother networks 412. The PSTN 408 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet410 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 412 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks412 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 404 or a different RAT.

Some or all of the WTRUs 402 a, 402 b, 402 c, 402 d in thecommunications system 400 may include multi-mode capabilities, i.e., theWTRUs 402 a, 402 b, 402 c, 402 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 402 c shown in FIG. 4A may be configured tocommunicate with the base station 414 a, which may employ acellular-based radio technology, and with the base station 414 b, whichmay employ an IEEE 802 radio technology.

FIG. 4B is a system diagram of an example WTRU 402. As shown in FIG. 4B,the WTRU 402 may include a processor 418, a transceiver 420, atransmit/receive element 422, a speaker/microphone 424, a keypad 426, adisplay/touchpad 428, non-removable memory 430, removable memory 432, apower source 434, a global positioning system (GPS) chipset 436, andother peripherals 438. It will be appreciated that the WTRU 402 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 418 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 418 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 402 to operate in a wirelessenvironment. The processor 418 may be coupled to the transceiver 420,which may be coupled to the transmit/receive element 422. While FIG. 4Bdepicts the processor 418 and the transceiver 420 as separatecomponents, it will be appreciated that the processor 418 and thetransceiver 420 may be integrated together in an electronic package orchip.

The transmit/receive element 422 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 414a) over the air interface 416. For example, in one embodiment, thetransmit/receive element 422 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 422 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 422 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 422 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 422 is depicted inFIG. 4B as a single element, the WTRU 402 may include any number oftransmit/receive elements 422. More specifically, the WTRU 402 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 402 mayinclude two or more transmit/receive elements 422 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 416.

The transceiver 420 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 422 and to demodulatethe signals that are received by the transmit/receive element 422. Asnoted above, the WTRU 402 may have multi-mode capabilities. Thus, thetransceiver 420 may include multiple transceivers for enabling the WTRU402 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 418 of the WTRU 402 may be coupled to, and may receiveuser input data from, the speaker/microphone 424, the keypad 426, and/orthe display/touchpad 428 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor418 may also output user data to the speaker/microphone 424, the keypad426, and/or the display/touchpad 428. In addition, the processor 418 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 430 and/or the removable memory 432.The non-removable memory 430 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 432 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 418 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 402, such as on a server or a home computer (notshown).

The processor 418 may receive power from the power source 434, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 402. The power source 434 may be any suitabledevice for powering the WTRU 402. For example, the power source 434 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 418 may also be coupled to the GPS chipset 436, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 402. In additionto, or in lieu of, the information from the GPS chipset 436, the WTRU402 may receive location information over the air interface 416 from abase station (e.g., base stations 414 a, 414 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 402 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 418 may further be coupled to other peripherals 438, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 438 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 4C is a system diagram of the RAN 404 and the core network 406according to an embodiment. The RAN 404 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 402 a, 402 b, 402 c over the air interface 416. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 402 a, 402 b, 402 c, the RAN 404, andthe core network 406 may be defined as reference points.

As shown in FIG. 4C, the RAN 404 may include base stations 440 a, 440 b,440 c, and an ASN gateway 442, though it will be appreciated that theRAN 404 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 440 a, 440 b,440 c may each be associated with a particular cell (not shown) in theRAN 404 and may each include one or more transceivers for communicatingwith the WTRUs 402 a, 402 b, 402 c over the air interface 416. In oneembodiment, the base stations 440 a, 440 b, 440 c may implement MIMOtechnology. Thus, the base station 440 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 402 a. The base stations 440 a, 440 b, 440 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 442 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 406, and the like.

The air interface 416 between the WTRUs 402 a, 402 b, 402 c and the RAN404 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 402 a, 402 b, 402 cmay establish a logical interface (not shown) with the core network 406.The logical interface between the WTRUs 402 a, 402 b, 402 c and the corenetwork 406 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 440 a, 440 b,440 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 440 a, 440 b,440 c and the ASN gateway 442 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs402 a, 402 b, 402 c.

As shown in FIG. 4C, the RAN 404 may be connected to the core network406. The communication link between the RAN 404 and the core network 406may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 406 may include a mobile IP home agent(MIP-HA) 444, an authentication, authorization, accounting (AAA) server446, and a gateway 448. While each of the foregoing elements aredepicted as part of the core network 406, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 402 a, 402 b, 402 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 444 may provide the WTRUs 402 a, 402b, 402 c with access to packet-switched networks, such as the Internet410, to facilitate communications between the WTRUs 402 a, 402 b, 402 cand IP-enabled devices. The AAA server 446 may be responsible for userauthentication and for supporting user services. The gateway 448 mayfacilitate interworking with other networks. For example, the gateway448 may provide the WTRUs 402 a, 402 b, 402 c with access tocircuit-switched networks, such as the PSTN 408, to facilitatecommunications between the WTRUs 402 a, 402 b, 402 c and traditionalland-line communications devices. In addition, the gateway 448 mayprovide the WTRUs 402 a, 402 b, 402 c with access to the networks 412,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 4C, it will be appreciated that the RAN 404may be connected to other ASNs and the core network 406 may be connectedto other core networks. The communication link between the RAN 404 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 402 a, 402 b, 402 cbetween the RAN 404 and the other ASNs. The communication link betweenthe core network 406 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

Other networks 412 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 460. The WLAN 460 may include anaccess router 465. The access router may contain gateway functionality.The access router 465 may be in communication with a plurality of accesspoints (APs) 470 a, 470 b. The communication between access router 465and APs 470 a, 470 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 470 a is in wirelesscommunication over an air interface with WTRU 402 d.

With the proliferation of personal mobile devices and applications suchas meters and sensors, it is expected that future WiFi systems andassociated APs will support a large number of devices, which may be muchmore than the current limit of 2007 devices per BSS. The 802.11ahstandard, for example, proposes supporting up to 6000 devices per BSS.

Channels allocated in the wireless spectrum may be limited in size andbandwidth. In addition, the spectrum may be fragmented in that availablechannels may not be adjacent to each other, and it may not be possibleto combine and support larger transmission bandwidths. Such is the case,for example, in spectrum allocated below 1 GHz in various countries.WLAN systems, for example built on the 802.11 standard, may be designedto operate in such spectrum. Given the limitations of such spectrum, theWLAN systems support smaller bandwidths and lower data rates compared tohigh throughput (HT)/very high throughput (VHT) WLAN systems, forexample, based on the 802.11n/802.11ac standards.

The spectrum allocation in some countries is limited. For example, inChina the 470-566 and 614-787 MHz bands only allow 1 MHz bandwidth.Therefore, there is a need to support a 1 MHz only option, in additionto supporting a 2 MHz option with a 1 MHz mode. The 802.11ah physicallayer (PHY) is required to support 1, 2, 4, 8, and 16 MHz bandwidths.

The 802.11ah PHY operates below 1 GHz and is based on the 802.11ac PHY.To accommodate the narrow bandwidths required by 802.11ah, the 802.11acPHY is down-clocked by a factor of 10. While support for 2, 4, 8, and 16MHz may be achieved by the 1/10 down-clocking, support for the 1 MHzbandwidth requires a new PHY definition with a Fast Fourier Transform(FFT) size of 32.

DCF performance deteriorates when a large number of STAs contend forchannel access. The overall number of medium access control (MAC)retries and the total transmission delay grows exponentially with thenumber of STAs contending for access. There are many scenarios in whicha WLAN system would encounter a large number of STAs simultaneouslyattempting to access the medium. For example, several key use cases havebeen defined for IEEE 802.11ah, including meters, sensors, and sensorbackhaul. When a WLAN BSS needs to support a very large number of STAs(e.g., 6000 STAs), it is likely that a group of STAs may wake upsimultaneously and try to access the medium simultaneously. Such ascenario may occur, for example, when a large number of STAs wake up andreceive the TIM transmission in the beacon, short beacon, or other typeof frame from the AP, and those STAs with a positive indication ofbuffered data/traffic contend for the medium to send a PS-Poll frame tothe AP.

Furthermore, in 802.11ai, one requirement is to support 100 STAssimultaneously entering a BSS and setting up fast initial link withinone second. To compete for access to the medium, each STA conducts arandom backoff by selecting a backoff number randomly from theContention Window (CW). Given that the STAs will have an initial CW sizeof seven, it is highly probable that packet collisions will take placewhen there are many more STAs in the WLAN. Since the 802.11 standardsprescribe that the CW size doubles each time a transmission is notsuccessful, the collision will likely occur for many rounds, dependingon the number of competing STAs. This repeated collision andretransmission process will cause the STAs to use a large amount ofenergy to deliver any packets, as well as cause large data delays andcongestion in the BSS. The issue for WLAN systems with a large number ofdevices is how to enhance DCF/EDCA to reduce channel contention andpacket collisions.

All existing power saving solutions/modes require keeping thedozing/sleeping STA in association with the AP to correctly receivetraffic indications in TIMs/DTIMs, as the Association IDs (AIDs) areused in identifying the corresponding traffic indication bits for theSTAs in the traffic indication bitmap in TIMs/DTIMs. The maximum numberof AIDs in the current dot11 specification is 2007; however, a WiFisystem may need to support a much larger number of devices (for example,802.11ah supports up to 6000 devices). There is a need to support morethan 2007 devices with the power saving mode in 802.11ah.

The current TIM transmissions as specified by the 802.11 standards havesome performance inefficiency. The current standards specify that theTIM contains the traffic indications for all STAs that have buffered BUsat the AP, regardless of the destination STA's status, i.e., in theactive state or the doze/sleep state. For the TIMs to include thetraffic indications for STAs in the doze/sleep state wastes resources,resulting in performance inefficiency for the TIM scheme. In particular,when required to support a large number of STAs in 802.11ah, the TIMencoding and transmission efficiency becomes a performance issue.

With DCF or PCF-CFP, for each positive traffic indication in a TIM, thefollow-up actions include a sequence of frame transmissions of PS-Pollfrom the STA to the AP and BU delivery from the AP to the STA or an ACKfrom the AP to the STA as a response to the PS-Poll. The maximum numberof PS-Poll+BU delivery/ACK sequences for a TIM interval is limited bythe TIM interval length, beacon frame size, channel bandwidth, sizes ofBUs, and rates/modulation coding sets (MCSs) used for BU transmissions.It is inefficient for the TIM to contain more positive trafficindications than the maximum number of PS-Poll+BU-delivery/ACK sequencesfor each TIM interval. This TIM transmission inefficiency becomes moresevere as the channel bandwidth decreases and/or the number of supportedSTAs increases. The issue for a WiFi system with a large number ofdevices is how to enhance the TIM protocol to allow for efficientoperation.

For a PCF-CFP BU transmission, there is a maximum number of BUs that canbe delivered during a TIM interval. If a TIM contains more positivetraffic indications than this maximum number, it leads to a potentiallylarger size TIM element; longer air time occupancy for transmission; andkeeping the STAs awake longer, resulting in power consumptioninefficiencies. As described above, in 802.11ah, the overhead of thebeacon frame with a TIM is 36.4%, not including the time used forchannel access and the inter-frame spacing. For the worst case, theoverhead of beacon frame would be 76.4% in a 100-ms beacon interval.Therefore, for a WiFi system with relatively small bandwidth butsupporting a large number of devices, an efficient method to signal apositive traffic indication in the TIM is needed.

A large number of devices may be supported and power savings may beachieved through collision reduction by controlled contention. Oneembodiment aims to provide energy saving mechanisms for a large numberof STAs by providing controlled contention to the medium and adaptingthe contention window (CW) size. In particular, the AP determines theinitial CW size depending on the expected load in the BSS. The STAsstill use carrier sense multiple access with collision avoidance(CSMA/CA) to contend for the medium, but the random backoff process ismodified for both associated STAs and unassociated STAs.

The AP may estimate how many STAs it must support either in its entireBSS or during a specific interval during the BSS operations. An exampleof such an interval is the interval after a TIM transmission in abeacon, short beacon, or other type of frame, which has a positiveindication of buffered data/traffic for a large number of STAs.

The initial CW size should be large enough to accommodate all STAs thatare expected to be operating within the interval for which the CW sizeis valid. The initial CW size should also provide extra space so thatany newly arrived STAs may be supported. The initial CW size may befixed for a BSS or it may vary for different intervals of the BSSoperation. For example, each beacon interval may have a differentinitial CW size depending on the number of STAs expected to operate inthat beacon interval. The initial CW size may be of the form of 2^(M)−1,where M is an integer and 2^(M)−1 may be larger than the number of STAsexpected to be operating in that beacon interval(s) or subinterval(s).

For example, up to 40 STAs which function as fire sensors may wake upsimultaneously to report that a fire has been detected. At the sametime, the AP needs to support 20 other STAs which stay active andoperate in the BSS. In addition, the AP could expect to supportassociation request frames from 10 new STAs. The initial CW size thenshould be larger than or equal to 70, depending on the implementation.

In another example, in a beacon interval, 100 STAs may be assigned towake up and compete for the medium. Such a situation may occur when alarge number of STAs wake up and receive a positive indication ofbuffered data/traffic in a TIM transmission from the AP, and these STAscontend for the medium to send a PS-Poll frame to the AP. In addition,the AP could expect to support association request frames from 15 newSTAs. The initial CW size then should be larger than or equal to 115,depending on the implementation.

Once the initial CW size is determined, it may be announced by the AP asa part of the beacon, short beacon, probe response, associationresponse, Fast Initial Link Setup (FILS) Discovery frame, or other typesof management or control frames. The CW size follows the same rule asprescribed in the 802.11 standards, and may be doubled every time atransmission fails. When a transmission is successful, the CW size mayrevert to a predetermined initial CW size.

The STAs may also be assigned a deterministic initial backoff number bythe AP at the time of association or at any other pre-negotiated time.For example, a deterministic initial backoff number/offset may beassigned to STAs by the AP before, after, or along with a TIMtransmission. The assignment of a back off number/offset to STAs by theAP may be carried out as a part of the beacon, short beacon, proberesponse, association response, or other new or existing management orcontrol frames. The assignment of the initial deterministic backoff maybe done in one or a combination of the following methods.

Method 1: The initial backoff numbers are sequential. For example, STA 1to STA 10 are assigned the backoff numbers n+1 . . . n+10 where n is anumber from the interval [0, 1, . . . , CW_size−10].

Method 2: The initial backoff numbers are randomly determined. Forexample, STA 1 to STA 10 are assigned a backoff number selected randomlyfrom the interval [0, 1, . . . , CW_size] with any probabilitydistribution. The selected backoff number should be ensured to be uniquefor each STA.

Method 3: The initial backoff numbers are randomly determined by adifferent method. For example, STA 1 to STA 10 are assigned the backoffnumbers N1, N1+n1, N1+n2, . . . , N1+n9, where n1, n2, . . . , n9 areunique and larger than 0.

Method 4: The AP assigns multiple initial backoff numbers to a STA ifthe STA has multiple packets to transmit. For example, the AP may assignthe backoff numbers [3, 3] to STA X, if STA X would likely be able totransmit twice during the controlled contention interval. In this case,the backoff number 6 (being equal to the backoff numbers [3, 3] assignedto STA X) should not be assigned to any other STA to avoid collisions.

The STAs with the assigned initial backoff number may attempt to accessthe medium using the initial CW size at a particular time. For example,sensor and meter STAs that are assigned to wake up in a particularbeacon interval may access the medium when the beacon interval startsfollowing a previously received beacon. In another example, STAs thatwake up and receive a positive indication of buffered data/traffic in aTIM transmission may access the medium following a beacon, short beacon,or other type of frame containing the TIM to send PS-Poll frames to theAP.

There are several classes of STAs. One class is TIM STAs, and if a TIMSTA is in the power saving mode, it will wake up at the assigned beaconintervals (according to the STA's sleep schedule) to listen to the TIM.If the TIM indicates that there is Buffered Unit (BU), the STA willretrieve the BU. Another class of STAs will not listen to the beacon orthe TIM, but will instead poll the AP for the BU whenever the STA wakesup.

In another example, an AP may indicate the start of a controlledcontention period using a control frame, a management frame, or othertype of frame, during which the STAs with an assigned initial backoffnumber may access the medium.

In one embodiment, shown in FIG. 5, the control frame may be a pollframe. An AP 502 sends TIM information 510 to a STA 504. The AP 502 thensends a poll frame 512 to the STA 504 that had a positive trafficindication in the TIM information 510. The poll frame 512 may be a newpoll frame for this protocol or the existing 802.11 PS-Poll frame,reused for this protocol. The format of the new poll frame may beassigned a new control subtype indication in the frame control field,and may include any one or more of: a frame control field with the newsubtype indication; an identification for the STA, such as its AID, MACaddress, etc.; or a BSSID, which is the address of the STA contained inthe AP. In response to the poll frame 512, the STA 504 sends a pollresponse frame 514 to the AP 502. The poll response frame 514 may be anyone of: the existing 802.11 PS-Poll frame, an ACK frame, or a short ACKframe.

In another variation, the AP may send a poll frame to a group of STAsthat had positive traffic indications in the TIM. This poll frame may bea new poll frame for this protocol or the existing 802.11 PS-Poll frame,reused for this protocol, but is either broadcast or multicast to agroup of users. The new poll frame may be the same as described above.In response to the poll frame from the AP, the group of polled STAs maytransmit according to their assigned backoff values. Each polled STAtransmits a poll response frame, which may be any one of: the existing802.11 PS-Poll frame, an ACK frame, or a short ACK frame.

In the cases of the AP polling a single STA and polling a group of STAs,the STAs from which PS-Polls were not received by the AP in the currentbeacon interval may be treated according to one or more of the followingrules.

1. The AP reschedules or reassigns the backoff numbers of those STAs inthe next or a subsequent beacon interval.

2. Those STAs receive a higher priority over STAs that receive anindication of buffered data/traffic in one of the next or subsequentbeacon intervals.

3. Those STAs maintain their assigned priority relative to STAs thatreceived an indication of buffered data/traffic in the same beaconinterval (e.g., by having deterministic backoff offsets that aresmaller).

In one embodiment, the AP may adjust the deterministic backoff offsetbased on the number of positive buffered data/traffic indications in theTIM broadcast. For example, if the number of indications is small, thebackoff offsets are smaller because there are fewer STAs competing formedium access. If the number of indications is large, the backoffoffsets are larger because there are more STAs competing for mediumaccess and there is a need to reduce collisions or congestion.

The AP may also indicate the start of a normal contention period afterthe controlled contention period using a schedule IE, field, subfield,or MAC/PLCP headers in a management, control, or other type of frame. ASTA may also choose to maintain this initial backoff number in anytransmissions and retransmissions following the initial medium access.The STA may also choose to follow the standard channel contention rulesusing the adaptive initial CW size and any CW size based on the initialCW size.

Alternatively, the backoff number for each STA may be implicitlydetermined by the order of its TIM indication. For each STA that has apositive indication in the TIM, the backoff number assigned to that STAmay be defined by a function of the order of the STA's positive TIMindication. For example, if a STA's positive indication is the k^(th)positive indication in the TIM, then the assigned backoff number forthat STA may be f(k). In another variation, the AP may determinesequences of backoff numbers Backoff_Seq(n, t), t≧0. A STA assigned tothe m^(th) backoff number sequence may use backoff_number=Backoff_seq(m,L) for the L^(th) time interval, where a time interval may refer to anytime interval such as beacon interval, beacon subinterval, wake up timeinterval, listening interval, a interval that has duration of a second,a millisecond or 100 milliseconds, etc. The assignment of the initialbackoff number “m” may implicitly indicate that the STA may use them^(th) Backoff_seq(m, t) for subsequent channel access. Differentbackoff number assignments for different channel access intervals maylead to fair power consumption and channel access for STAs.

The assigned initial backoff number/values may also be implemented as aschedule, either dynamic or static. For example, each of the initialbackoff numbers/values may have an implicit associated time unit (TU) tocomprise an actual backoff time defined as the time that a STA may waitbefore attempting channel access. The TU may be implemented as a slottime or any other units of time. For example, if the TU is K ms and STA1 to STA 10 are assigned the backoff numbers n+1 . . . n+10, then theactual backoff times of STA1 to STA10 are (n+1)×K, . . . (n+10)×K ms,respectively. In the case of a TIM-based DL data retrieval scenario, thesequence of STAs that are assigned backoff numbers is signaledimplicitly by the TIM bitmap based on the STA's position within the TIMbitmap. The value of the implicit TU for each STA or each backoff numberis either fixed, for example, in the specification, or is signaled as apart of the beacon, short beacon, probe response, association response,FILS Discovery frame, or other new or existing management or controlframes.

Another embodiment is to use a hash function with STA-specific andAP/BSS-specific parameters to determine the backoff time for each STAwith a positive indication in the TIM. Using the hash function makes thebackoff time different across different APs in the overlapping BSS(OBSS) and different for STAs in different beacon intervals, to havesome fairness in the DL data retrieval latency across APs. TheSTA-specific and AP/BSS-specific parameters used to determine thebackoff time may be one, or a combination of several parameters,including the following: the BSSID (or the MAC address) of the BSS/APthat transmits the TIM; the AID/MAC address of the STA with a positiveTIM indication; the bitmap position within the TIM; the TSF value of theAP with which STA is associated; the OBSS/neighbor AP TSF offset, withrespect to the TSF of the AP with which STA is associated; the slottime; or the total number of positive TIM indications of a BSS or OBSS.

For example, the backoff time of each STA i with a positive TIMindication, denoted by TBO(i), may be given by:TBO(i)=Hash(bitmap position,BSSID,AID,TSF)  Equation (1)

In both methods (sequential allocation and hash function), if thecalculated backoff time falls into a beacon transmission time or arestricted access window (RAW) that it is not allowed to use, then thecalculated backoff time is adjusted accordingly. One way is to postponethe backoff time by the amount of conflicting beacon transmission time(denoted as TBeacon) or not allowed RAW duration (denoted as TRAW):TBO(i)=TBO(i)+TBeacon or TBO(i)=TBO(i)+TRAW   Equation (2)

In some scenarios, there may be a limit on the maximum backoff time, forexample, Tmax. Then TBO(i) is given by:TBO(i)=max(Tmax,Hash(bitmap position,BSSID,AID,TSF))   Equation (3)

The value of Tmax may be chosen by the AP, considering factors such asthe DL data retrieval time window or the beacon interval. For example,if the beacon interval is 500 ms, the AP wants to restrict the backofftime to within one beacon interval, the beacon transmission time is 50ms, and the time unit (TU) is 20 ms (i.e., K=20). Then, Tmax may bechosen to be 450 ms (500 ms−50 ms) or 430 ms (500 ms−50 ms−20 ms). Orthe AP may choose to reserve 250 ms out of the 450 ms for DL dataretrieval and UL PS-Poll/trigger frames, then Tmax may be chosen to be250 ms or 230 ms.

Alternatively, to enhance efficiency, especially in the case where theSTA sends a PS-Poll in the UL to retrieve DL data, a dynamic value ofthe associated TU may be used for each STA that receives a positive dataindication in the TIM. For each positive indication in the TIM, aninformation field of the associated dynamic TU with M bits is alsocarried in the same frame, where the TIM is transmitted to represent thedynamic value of the associated TU, or a frame immediately after theframe containing the TIM. As shown in FIG. 6, an implicit one-to-onemapping between the positive indication in the TIM 600 and theassociated TU is decided by the order of the positive indication in TIMand the order of the TU fields. For example, a positive indication in afirst bit position 602 corresponds to a TU 604 associated with the firstbit position.

The actual backoff time may be calculated using the dynamic TU valuesfor each STA. In one option, the actual backoff time is the STA'sbackoff value multiplied by the associated TU. For example, STA 1 to STA10 are assigned the backoff numbers n+1 . . . n+10, and associated TU1,. . . , TU10. Then the actual backoff values of STA1 to STA10 are(n+1)×TU1, (n+2)×TU2, . . . , (n+10)×TU10 ms, respectively.

In a second option, the actual backoff time is the first backoff time(backoff value multiplied by associated TU) plus other subsequentassociated TUs up to the STA of interest. For example, STA 1 to STA 10are assigned the backoff numbers n+1 . . . n+10, and associated TU1, . .. , TU10. Then the actual backoff values of STA1 to STA10 are (n+1)×TU1,(n+1)×TU1+TU2, . . . , (n+1)×TU1+sum (TU2, . . . , TU10) ms,respectively.

If the calculated backoff time of a STA falls into a beacon transmissiontime or a RAW that it is not allowed to use, then the calculated backofftime is adjusted accordingly, as in the case of fixed TUs describedabove.

The value of the associated TU is chosen to be large enough to cover theframes of PS-Poll+SIFS+DATA+SIFS+ACK (or short ACK). The reason that adifferent TU may be used is because each STA may have a different amountof data and a different ACK policy (for example, a short ACK versus aregular ACK). A predetermined range of the associated TU (such asK_(min) to K_(max) ms) may be used, and the M bits value represents auniformly quantized TU. That is, 2M levels of uniform quantization isapplied to the K_(min) to K_(max) ms.

The AP may signal a positive data indication for STAs that have downlinkdata buffered at the AP using a TIM bitmap. It may then assign aninitial backoff number to STAs and include these assignments in unicast,broadcast management, or control frames, such as a TIM-carrying frame,association response, or other management or control frames. In the caseof a TIM-based DL data retrieval scenario, the sequence of STAs that areassigned backoff numbers is signaled implicitly by the TIM bitmap. Forthe case of a dynamic TU, the AP may calculate the appropriate value ofthe associated TU for each STA that has a positive data indication inthe TIM bitmap.

The AP may then transmit the following information (fields) in thebeacon, in addition to the TIM: the associated TU values for each STAthat has a positive data indication in the TIM bitmap, and it mayinclude schedules for the controlled contention period, contention-freeperiod, contention-based period, and the like. In the case of aTIM-based DL data retrieval scenario, the AP may choose to transmitbuffered downlink packets to a STA when the STA transmits a UL packet,such as a PS-Poll or other trigger packet/frame.

FIG. 7 is a flowchart of a method 700 for a STA to transmit packets. TheSTA may wake up at the start of the controlled contention period, beaconinterval, or beacon subinterval (step 702). The STA checks whether ithas any UL data packets to transmit (step 704). If there are no UL datapackets to transmit, then the STA goes back to sleep (step 706) and themethod terminates (step 708).

If the STA has UL data packets to transmit (step 704), then adetermination is made whether the STA's backoff time has expired (step710). If not, then the STA sleeps until the backoff time expires (step712). After the STA's backoff time has expired (steps 710 or 712), thenthe STA starts channel access to transmit its UL data packets (step714). The STA then goes back to sleep (step 706) and the methodterminates (step 708).

FIG. 8 is a flowchart of a method 800 for a STA to retrieve packetswaiting for it. The STA wakes (step 802) and listens to the TIM in thebeacon (step 804). A determination is made whether there is a positivetraffic indication for the STA in the TIM (step 806). If there is not apositive traffic indication for the STA in the TIM, then the STA goesback to sleep (step 808) and the method terminates (step 810).

If there is a positive traffic indication for the STA in the TIM (step806), then a determination is made whether the STA has fixed associatedTU (step 812). If the STA does not used a fixed associated TU, meaningthat the STA uses a dynamic associated TU, then the STA obtains thevalue of its associated TU (or all associated TUs of STAs up to itselfin the TIM bitmap order) (step 814). If the STA has a fixed associatedTU (step 812) or after the STA obtains the value of the TU (step 814),the STA calculates its backoff time (step 816).

The STA then sleeps until its backoff time expires (step 818). The STAthen wakes up to retrieve its DL data (step 820). To retrieve the DLdata, the STA may send a PS-Poll or other triggering frame to the AP.After retrieving the DL data, the STA goes back to sleep (step 808) andthe method terminates (step 810).

For STAs that have not associated with the AP, the initial backoffassignment is more difficult, because no link has been set up betweenthe STAs and the AP. The AP may include in its beacon, probe response,or other broadcast, multicast, or unicast frames the followinginformation: the initial CW size and the initial backoff ranges thathave not been assigned by the AP to the STAs that are already associatedwith the AP. The unassociated STAs may adapt the initial CW size andrandomly pick an initial backoff number and then use these parameters toaccess the medium to associate with the AP.

The controlled contention period may be scheduled a priori by a scheduleIE included in the beacon or other management/control frames. To reducecollisions caused by STAs in the OBSS or by newly arrived STAs that areunaware of the scheduling of the controlled contention period,additional medium reservation may be performed by the AP using thefollowing methods.

Method 1: The AP signals the start of the controlled contention periodby transmitting a CTS-to-BSS, which is a standard clear to send (CTS)frame with the receiver address (RA) set to a broadcast/multicastaddress that is agreed upon for the specific BSS. The duration field ofthe CTS frame is set to equal to the controlled contention period. AllSTAs that are not part of the BSS set their network allocation vector(NAV) until the end of the contention period, while the STAs in the sameBSS may conduct the controlled contention access to the medium.

Method 2: The AP assigns the controlled contention period to startimmediately after a beacon, a short beacon, or other type of managementor control frame. The duration field of the beacon, short beacon, orother type of management or control frame may be used to set the NAV forthe controlled contention period. The beacon, short beacon, or othertype of management or control frame also includes schedule informationsuch as an IE, field, or subfield to announce to all STAs in the BSSthat the controlled contention period will start immediately after thebeacon. When a STA receives a beacon from the AP in the BSS, it ignoresthe NAV setting of the beacon if the beacon also contains a schedule IEfor a controlled contention period immediately following the beacon.

The AP/STA behavior, procedures, and associated signaling may beimplemented in a variety of ways. For example, the signaling may beimplemented as an IE, a field, or a subfield that are new or existing, apart of MAC/PLCP headers in any type of management, control, or othertype of frame. The initial CW size, as well as the initial backoffnumber assigned, may be conveyed to one or more STAs using signalingsuch as the Backoff IE, which may be included in beacon, associationresponse, and other broadcast, multicast, or unicast management orcontrol frames.

An example of the Backoff IE format is shown in FIG. 9. The Backoff IE900 may include the following fields: element ID 902, length 904, MAP906, initial CW_size 908, maximum CW_size 910, initial backoff number912, and other optional information 914. The element ID field 902includes an ID to identify that this is a Backoff IE. The length field904 is the length in octets of the remainder of the IE. The MAP field906 indicates the mandatory and optional information contained in theIE. The initial CW_size field 908 is the size of the initial CW that aSTA should adapt, and is a mandatory field. The maximum CW_size field910 is the maximum size of the CW that a STA should adapt, and is anoptional field.

The initial backoff number field 912 contains one or multiple initialbackoff number(s) assigned to a particular STA. This field is optionaland is only included in a unicast frame addressed to one particular STA,for example, in an association response frame or a unicast management orcontrol frame. Alternatively, a field may also be included for one ormore STAs that include the assigned initial backoff number. The fieldmay include the IDs for the STAs, such as the AID, MAC addresses, etc.The field may include just the assigned initial backoff numbers for agroup of STAs if the IDs of the STAs are implicitly determined. Forexample, if the assigned initial backoff numbers are provided for apre-determined group of STAs and the order of the STAs in the group ispre-determined as well, each STA may obtain the assigned initial backoffnumber according to its order in the group.

The other optional information field 914 contains other optionalinformation, for example, the range of the unassigned (and thereforestill available) backoff numbers in the form of the interval[Start_value, End_value] or other forms, any announcement of multipleelements of initial backoff number assignments, or the duration forwhich the Backoff IE 900 is valid.

The schedule of the various intervals including the controlledcontention interval may be conveyed to the STAs by the AP using theInterval Schedule IE which may be included in beacon, associationresponse, or other management or control frames. An example of theInterval Schedule IE format is shown in FIG. 10.

The Interval Schedule IE 1000 may include the following fields: elementID 1002, length 1004, MAP 1006, schedule type 1008, start time 1010, endtime 1012, and other optional information 1014. The element ID field1002 includes an ID to identify that this is an Interval Schedule IE.The length field 1004 is the length in octets of the remainder of theIE. The MAP field 1006 indicates the mandatory and optional informationcontained in the IE. The schedule type field 1008 is the schedule is forcontention-free interval, controlled contention interval,contention-based interval, etc. The start time field 1010 is the starttime of the scheduled interval, counting from the end of the currentframe. The end time field 1012 is the end time of the scheduledinterval, counting from the end of the current frame.

The other optional information field 1014 includes any one or more ofthe following: repeat frequency, whether this applies to, for example,all following beacon intervals until further notice; and CW sizes,initial backoff number, or unassigned backoff number range that appliesfor the scheduled interval.

The CTS-to-BSS may be used by the AP to conduct medium reservation tosignal the start of the controlled contention period. The CTS-to-BSS isa standard CTS frame with the RA set to some broadcast/multicast/unicastaddress that is agreed upon for the specific BSS. The duration field ofthe CTS frame should be set to equal to the controlled contentionperiod. All STAs that are not part of the BSS set their NAV to the endof the contention period, while the STAs in the same BSS may conduct thecontrolled contention access to the medium.

The AP calculates the initial CW size based on the expected number ofSTAs that need to be supported in the BSS or in the specific interval,such as a specific beacon interval. The AP assigns an initial backoffnumber to the STAs and includes these assignments in unicast, broadcastmanagement, or control frames such as association response or othermanagement or control frames. The AP assigns itself one or more initialbackoff numbers for DL transmissions.

The AP transmits the following information (fields) in the beacon orshort beacon: the initial CW size to be used, the duration for which theinitial CW size is valid, the unassigned backoff value interval forunassociated STAs, a newly assigned or changed backoff number forassociated STAs. The beacon optionally includes schedules for thecontrolled contention period, contention-free period, contention-basedperiod, etc. The AP may also optionally transmit a CTS-to-BSS toindicate the start of the controlled contention period and to reservethe medium. The AP may choose to transmit buffered DL packets to a STAwhen the STA transmits UL packets.

The STA's behavior during the controlled contention period may includewaking up at the start of the controlled contention period. If the STAhas no packets to transmit, then the STA goes back to sleep.Alternatively, the STA may also choose to wake up during a normalcontention period later if a packet has arrived for transmission duringthe controlled contention period. In the normal contention period, theSTA uses the adaptive CW size and may choose to maintain its assignedinitial backoff number or follow the normal random backoff procedure. Ifno transmission is detected on the medium, the STA waits for a DIFStime, then starts to count down using the initial backoff number(s)assigned to it by the AP.

If the STA counts down to zero and there is no transmission detected onthe medium, then the STA transmits the packet. If the transmission issuccessful, and there are no more packets to transmit, the STA returnsto sleep until the next scheduled wake up interval or until the nextscheduled contention period. If the transmission is not successful, orif there are more packets to transmit, then the STA uses the additionalassigned backoff number in the controlled contention period.Alternatively, the STA may also elect to sleep until the next controlledcontention period or normal contention period to transmit the packets.

If the STA has not counted down to zero and transmission is detected onthe medium, then if the preamble can be decoded, the STA calculates thelength of the packet and returns to sleep until waking up at the end ofthe ongoing packet. If the preamble cannot be decoded, the STA sleepsfor the duration of the shortest packet possible and wakes up to conductCCA again. If the medium becomes idle, the STA waits for a DIFS time andstarts counting down again.

During the controlled contention interval, the AP's and STAs' behaviorsare illustrated in FIG. 11 as examples. In FIG. 11, the AP indicates thestart of the controlled contention period by sending out a CTS-to-BSS(1102), or other type of management or control frame which may alsoreserve the medium for the duration of the controlled contention period.STA1, STA2, STA3, STA5 are already associated with the AP; STA4 justarrived in the BSS and is looking to associate with the AP. The backoffnumber assignments for STA1, STA2, STA3 and STA5 are as follows: STA1:1; STA2: [2,4], which are two backoff numbers for more frequent accessto the medium during the controlled contention interval; STA3: 4; andSTA5: 5. The unassigned backoff number 4 is announced in the beacon andSTA4 randomly selects 4 as its backoff number.

The controlled contention illustrated in FIG. 11 operates as follows.STA5 does not have any packets to transmit during this controlledcontention period, so it goes to sleep immediately (1104). All STAs withpackets to transmit wait for a DIFS period (1106) and start to countdown.

STA1 counts down one slot and starts to transmit its packets (1108). Allother STAs sleep after decoding the preamble of the frame transmitted bySTA1 (1110). STA1 goes to sleep after completing its frame transmission(1112) until the next scheduled interval.

STA2 counts down one slot and starts to transmit its packets (1114). Allother STAs sleep after decoding the preamble of the frame transmitted bySTA2 (1116). Since STA2 is assigned two backoff numbers and it haspackets to transmit, it will continue participate in the controlledcontention process.

STA4 counts down one slot and starts to transmit its packets (1118). Allother STAs sleep after decoding the preamble of the frame transmitted bySTA4 (1120). STA4 goes to sleep after completing its frame transmission(1122) until the next scheduled interval.

STA3 counts down one slot and starts to transmit its packets (1124). Allother STAs sleep after decoding the preamble of the frame transmitted bySTA3 (1126). STA3 goes to sleep after completing its frame transmission(1128) until the next scheduled interval.

STA2 counts down two slots and starts to transmit its remaining packets(1130). All other STAs sleep after decoding the preamble of the frametransmitted by STA2.

A large number of devices may be supported through a registered-statebased power saving mode. A new power saving mode, the Registered-StateBased (RSB) Power Save (PS) mode, is defined, which is an efficientmethod to notify a large number of devices/STAs that have data bufferedat the AP.

When there are a large number of STAs (for example, 6000 STAs, which ismore than what the current AID limit of 2007 can support), a new state(the “Registered State”) is supported in the BSS. Logically, a STA inthe Registered State is associated and authenticated with the AP, i.e.,it allows all three classes of frames. But it does not need to have anAID assigned, although it may have an AID. When in the power savingmode, the STA in the Registered State does not need to perform securitykey updates. For a STA to enter the Registered State, it exchangesregistration information (for example, the STA sends RSB-PS operationparameters, e.g., sleep cycle, to the AP and receives a RegistrationIdentifier (RID) assignment) with the AP using MAC management frames,for example, public management frames. The AP manages and assigns theRID to a STA requesting to register with the AP in supporting the RSB-PSmode. The size of the RID is determined by the number of STAs that needto be supported in the Registration State by an AP.

When there is data for an STA in the Registered State, the AP may sendthe STA traffic indications corresponding to the RID to indicate ifthere are buffered BUs. Upon receiving a traffic indication of data, theSTA in the Registered State takes actions to receive the data from theAP. If the STA in the Registered State has data to transmit, then ittakes action to send the data.

The AP may also initiate a state change procedure to request a STA inthe associated mode to change to a Registered State. This may beinitiated by an AP based on the traffic behavior exhibited by the STAand to manage system resources. The AP may decide to make such a STAstate change, for example, to release AIDs given that AIDs are limitedin number. The AP may send the state change request to a STA in anyframe, such as a management frame. For example, an existing managementframe may be modified to include this request or a new management framemay be used for this purpose. If such a STA state change is negotiatedsuccessfully, the STA exchanges registration information (for example,the STA sends RSB-PS operation parameters, e.g., sleep cycle, to the APand receives a RID assignment) with the AP.

The STAs in the Registered State are organized into Traffic IndicationGroups (TIGs) when in the power saving operation. The STAs in the sameTIG are signaled with their traffic indications in the same trafficindication IE. Each TIG is assigned a unique identifier, called TrafficIndication Group ID (TIG-ID), within the BSS domain. The size of theTIGs, i.e., the number of STAs in a group and the length of the TIG-ID,i.e., the number of groups, depend on the grouping criteria, trafficindication interval, the capability of BU delivery in a trafficindication interval, and the total number of STAs supported by thesystem. These may be specified as system parameters with a fixed valueor configurable system parameters managed through Management InformationBases (MIBs). For example, such information may be configured andbroadcast by the AP in frames such as beacons and probe responses.

The grouping criteria may be based on the sleep cycle, delay tolerance,traffic patterns, device ownership, STA type (for example,meters/sensors), applications, locations, etc.

One STA may be assigned to one TIG or multiple TIGs. For example, iftraffic patterns are used as grouping criteria, and a STA supportsmultiple applications with different traffic characteristics, then theSTA may be assigned to two different TIGs, one for each application.

For the convenience of illustration, the case where one registered STAis assigned to only one group is used as an example herein.

When in the RSB-PS mode, a STA is identified by a unique RID within theBSS domain. The RID of a STA consists of its TIG-ID and itsidentification within the TIG, the In-Group STA ID (IG-SID). Similar tothe TIG-ID, the size of RID and the size of the IG-SID may be specifiedas system parameters with fixed values or as configurable systemparameters managed through MIBs. For example, such information may beconfigured and broadcast by the AP in frames such as beacons and proberesponses. The RID (instead of the AID) is used in the RSB-PS mode toencode/decode traffic indications for registered STAs. A STA in theregistered state may not have an AID assigned.

FIG. 12 shows an example of the RID format 1200, where the RID is twobytes, in which the ten most significant bits (MSBs) are the TIG-ID1202, and the six least significant bits (LSBs) are the IG-SID 1204.Other lengths of the RID format 1200 (and corresponding combinations ofTIG-ID 1202 and IG-SID 1204 lengths) are possible. A RID identifies aunique STA within the BSS domain. With the example of the 16-bit RID, amaximum number of 64K stations may be supported per BSS.

To support the RSB-PS mode, a new traffic indication IE, called theRID-TIM IE, is defined to use the RID to signal the traffic indicationsfor the STAs with buffered BUs at the AP. The RID-based TIM elementdesign includes: one RID-based TIM element for one TIG; an informationfield to signal the TIG-ID; a partial virtual bitmap to signal thetraffic indications for the STAs in the TIG; and indication informationto identify the presence of bitmap bytes in the partial virtual bitmap,to minimize the size of the RID-TIM element.

FIG. 13 shows an example of the RID-based TIM element format 1300, wherethe RID 1302 is 16 bits with a 10-bit TIG-ID field 1304 and a six-bitIG-SID 1306. In the RID-based TIM element shown in FIG. 13, theinformation fields, element ID, length, DTIM count, and DTIM period arekept the same as the current TIM element as specified by the 802.11standards, except that a new element ID value is assigned to identifythe RID-based TIM element. The 10-bit TIG-ID field 1304 is used toidentify the TIG that the RID-TIM element is intended for. For a six-bitIG-SID 1306, there are a maximum of 64 STAs in a TIG. This determinesthat the full bitmap for 64 STAs will have 64 bits, i.e., eight bytes.To improve the efficiency of the RID-TIM element, not all the eightbytes in the full bitmap are included in the RID-TIM. Instead, a partialvirtual bitmap field is used with the length of one to eight bytes. Sucha partial virtual bitmap field structure is specified by otherinformation field(s) in the RID-TIM element. For example, as shown inFIG. 13, two index fields, called First Bitmap Byte Index (FBBI) 1308and Last Bitmap Byte Index (LBBI) 1310, indicate the first and the lastbitmap bytes in the partial virtual bitmap field 1312, respectively. Thebitmap bytes before the FBBI 1308 are all of the value zero, and so arethe bitmap bytes after the LBBI 1310. For example, for the followinggiven full bitmap:

Byte- 0 Byte-1 Byte-2 Byte-3 Byte-4 Byte-5 Byte-6 Byte-7 0x00 0x00 0xA10x00 0x58 0xF3 0x00 0x00

The values of FBBI, LBBI, and the partial virtual bitmap are:

FBBI=0b010

LBBI=0b101

Partial virtual bitmap=0xA1 0x00 0x58 0xF3

Alternatively, instead of using two byte-index fields in the RID-basedTIM element to identify the structure of the partial virtual bitmap, abitmap control field may be used to indicate the presence of the trafficindication bitmap bytes in the partial virtual bitmap field. Each bit inthe control field corresponds to a bitmap byte index in the full TIMbitmap. A value of one indicates “present” as at least one bit in theTIM bitmap byte is non-zero; and a value of zero indicates “not present”as all the bits in the corresponding bitmap byte are zero. In this way,the partial virtual bitmap field contains only the bitmap bytes withnon-zero values.

FIG. 14 shows an example of a RID-based TIM element 1400 with a bitmapcontrol field 1402 for the partial virtual bitmap 1404. Using the sameexample of a given full bitmap, i.e.,

Byte- 0 Byte-1 Byte-2 Byte-3 Byte-4 Byte-5 Byte-6 Byte-7 0x00 0x00 0xA10x00 0x58 0xF3 0x00 0x00

The values of the bitmap control field 1402 and the partial virtualbitmap 1404 are:

Bitmap Control=0b00101100

Partial virtual bitmap=0xA1 0x58 0xF3

In addition, the RID-based TIM element may be further improved for theTIG based on multicast traffic indication, by using one control bit toindicate the multicast traffic in the group and having an empty partialvirtual bitmap (i.e., zero bytes), instead of including a full bitmapwith all “1”s.

The RID-based TIM element supports up to 64K STAs. It provides anefficient method to notify the STAs that have data buffered at the AP bygrouping the STAs. The STAs may be grouped based on, for example, thetraffic patterns, the BU delivery capability in the traffic indicationinterval, etc. The RID-based TIM element achieves a performanceenhancement when it is applied to the STA status-based RID-TIM scheme,as described below.

The RID-based TIM element may be used in the management frames where thecurrent TIM element may appear, for example, a beacon frame, a TIMbroadcast frame, etc. Depending on the STAs and their applications in aBSS, the RID-based TIM element may co-exist with the current TIM elementin the same management frame or may be used alone by itself in themanagement frames. Also, in addition to the current management frames,the RID-based TIM element may also be used in a new management frame.

The RID-based TIM element is for an individually addressed trafficindication and TIG-based multicast traffic indication. To supportbroadcast traffic and non-TIG-based multicast traffic indication anddelivery, one method is to use the current broadcast/multicast trafficindication/delivery schemes, e.g., the DTIM scheme, as specified in thecurrent 802.11 standards. Alternatively, a new method may be based onthe RID to support broadcast traffic and non-TIG-based multicast trafficindication and delivery in the RSB-PS mode.

Special TIG IDs are reserved to indicate broadcast traffic andnon-TIG-based multicast traffic. Table 1 shows an example using the16-bit RID with a 10-bit TIG-ID and a 6-bit IG-SID.

TABLE 1 RID-Based Broadcast/Multicast Identifications Registration ID(RID) TIG IG-SID Descriptions 0b0000 0000 00 any Unicast RIDs, used toidentify to individually addressed STAs for 0b1111 1111 01 DL trafficindications. 0b1111 1111 10 Multicast Multicast RIDs (MRIDs), used to IDidentify multicast groups for DL multicast traffic indications. 0b11111111 11 Not used, Broadcast RID (BRID), used for set to all 0s broadcasttraffic indications.

The multicast group is different from the TIG, as the multicast group isused for multicast data delivery, while the TIG is used for trafficindication, not for traffic delivery. A multicast group may contain anynumber of STAs, and it is formed and maintained through correspondingprocedures and rules. There may be multiple multicast groups, eachidentified by a unique Multicast ID (MID) within a BSS domain.

The STA status information may also be used to further improve theefficiency of the RID-TIM, called a STA status based RID-TIM. TheRegistered STAs may be grouped based on their listening windows, wherethe listening window means the time duration in which the STA is in thelistening status. The AP uses the STA status information to assemble thepartial virtual bitmap in the RID-TIM element for the STAs in the RSB-PSmode, so that the partial virtual bitmap only contains the positivetraffic indications for the STAs in the listening status at the timewhen the frame containing the RID-TIM element is transmitted. When theSTA status information is used to group the STAs in the RSB-PS mode, theSTAs with positive traffic indications at a given time are furtherclustered under the same TIG, resulting in an efficient use of theRID-TIM scheme.

Similar to the current 802.11 power saving mode operation, a DL BUdelivery request signal may be used in the RSB-PS mode for the STAs torequest the delivery of the buffered BUs, after receiving positivetraffic indications in the RID-TIMs. The current PS-Poll control framecannot be used for the RSB-PS mode, because it uses the AID in its MACheader, while a STA in RSB-PS mode may not have an AID. Two solutionsare proposed to address this DL BU delivery request signaling issue inRSB-PS mode.

A new control frame, the RSB-PS-Poll frame, is defined for the STAs inthe RSB-PS mode to request DL BU delivery after receiving a positivetraffic indication in the RID-TIM, by using one of the reserved controlframe subtype values. The RSB-PS-Poll frame may have the same format asthe PS-Poll frame, except that the ID field in the MAC header is set tothe RID of the transmitting STA, instead of the AID.

The STAs in RSB-PS mode use the current PS-Poll control frame to requestDL BU delivery after receiving a positive traffic indication in theRID-TIM by setting the ID field in its MAC to an invalid AID value. Whenthe AP receives a PS-Poll frame with an invalid value in the ID field,it ignores the ID field, and uses the source MAC address field toidentify the transmitting STA of the PS-Poll frame.

The following solutions relate to the address issues when using the PSMP(Power Saving Multi-Poll) scheme for the STAs in the RSB-PS mode, as thecurrent PSMP scheme specified in the 802.11 standards uses the AID toidentify the STAs for the DTT (Downlink Transmission Time) and UTT(Uplink Transmission Time) allocations. But, the STAs in the RSB-PS modemay not have AID assigned.

A new PSMP frame, the RSB-PSMP frame, is defined by assigning a new HTAction code point. The RSB-PSMP frame may have the same format as thePSMP frame specified in the current 802.11 standards, except that the16-bit STA-ID field is set to the RID, instead of the AID.Alternatively, the current PSMP frame is used by assigning a new STAInfo Type value to identify the STAs in the RSB-PS mode, and alsosetting the STA-ID filed to the RID, not the AID.

An authenticated/associated STA in the RSB-PS mode is assigned a RID bythe AP in the BSS, then the STA is “registered” with the AP. The RIDassignment may be done by including a new IE, the RID assignmentelement, in an association response management frame or a new MACmanagement frame.

The RSB-PS mode may use the same operation parameters, for example,ListenInterval, ReceiveDTIMs, etc., as specified and signaled in thecurrent 802.11 standards. Alternatively, the RSB-PS mode operationparameters may be configured and signaled by a new set of MAC sublayermanagement entity (MLME) primitives and IEs included in existing or newmanagement frames at the time the RID is assigned. Such a new set ofpower saving parameters may allow different ranges of values, forexample, a longer sleep interval.

Before or at registration, the RSB-PS capability may be communicatedbetween the AP and the STA through either an explicit RSB-PS capabilityindication or an implicit signaling mechanism, for example, RSB-PSparameter negotiation and acknowledgement. After registration, the STAis ready for RSB-PS mode operation.

A registered STA needs to follow the entering RSB-PS mode procedure toenter the RSB-PS mode operation. A registered STA may enter the RSB-PSmode by using the current procedures for entering the power save mode,i.e., by using the power management subfield in the frame control fieldin the MAC header.

Alternatively, entering the RSB-PS mode may be based on an explicithandshaking procedure. For example, a set of new MAC management framesmay be introduced to request/response or command/acknowledge the entryof the RSB-PS mode operation. The handshaking procedure may also includethe RID assignment and the RSB-PS operation parameter setup, such thatall the steps of initializing the RSB-PS mode operation are conducted inthe same procedure.

The RSB-PS mode operation does not need the AID. When entering theRSB-PS mode, the AID of the STA may be released or it may be kept. Ifkept, nothing about the AID needs to be done. If the AID is released, itmay be released implicitly by a successful entry to the RSB-PS mode whenthe RSB-PS mode is configured to always release the AID when enteringthe RSB-PS mode. Alternatively, releasing the AID may be done explicitlyby including an AID release indicator in the signaling of entering theRSB-PS mode procedure. A released AID may be re-assigned to other STAs.

Similar to the current PS (Power Saving) mode operation, a STA in theRSB-PS mode alternates between an available (also called listening orawake) state and not-available (also called not-listening or doze)state. When in the not-available state, the STA may partially or fullyturn off its transmitter and receiver to save power. The operationprocedures of the RSB-PS mode and the current PS mode have somedifferences, mainly because a STA in the RSB-PS mode may not have an AIDassigned, while the AIDs are used in the current PS mode operations. Inaddition, a longer doze interval may be supported by the RSB-PS mode, ascompared to the PS mode.

The following describes the differences of the RSB-PS mode operationfrom the PS mode operation.

DL traffic indication: The RID-TIM element is used for the STAs inRSB-PS mode.

DL buffered BUs delivery: The RID-based PS-Poll control frame, e.g., theRID-PS-Poll, is used for the STA in the RSB-PS mode to request thebuffered BUs delivery from the AP, after receiving a positive trafficindication for it. Alternatively, the AP may deliver the DL buffered BUsimmediately after sending the traffic indications, without waiting for arequest, e.g., RID-PS-Poll, from the STA, particularly when using theSTA status-based traffic indication scheme.

DL buffered broadcast/multicast BUs delivery: To support more efficientpower savings by allowing long doze intervals, the STAs in the RSB-PSmode may not need to wake up based on the signaled broadcast/multicasttraffic indication/delivery intervals, for example, the DTIM interval.Instead, the buffered broadcast/multicast BUs may be delivered on a TIGbasis only when the STAs are in their listening window. Alternatively,it may depend on the applications or upper layers of thebroadcast/multicast BUs to handle the synchronizations needed in thebroadcast/multicast data communications.

UL traffic transmission: A STA in the RSB-PS mode may wake up at anytime during its doze interval when it has UL data to transmit.Alternatively, it may also buffer the UL BUs until its next periodiclistening window.

Security key update: To support a long doze interval, particularly aperiod longer than some security key refreshing interval (if any), a STAin the RSB-PS mode may not need to wake up just for key refreshment.Instead, the key updates may be conducted the next time the STA entersits listening window or wakes up for its UL data transmission. In thiscase, certain signaling supports may be used to accelerate the keyrefreshment, for example, including key update information in the DLtraffic indication or PS-Poll control signal.

When applying the PSMP (Power Saving Multi-Poll) scheme to the STAs inRSB-PS mode, the RID based PSMP scheme is used.

A STA in the RSB-PS mode may terminate its RSB-PS mode operation byusing the current terminating PS operation procedure, i.e., by using thepower management subfield in the frame control field in the MAC header.Alternatively, the termination of the RSB-PS mode may be based on anexplicit handshaking procedure, for example, a set of new MAC managementframes are introduced to request/response or command/acknowledge thetermination of the RSB-PS mode operation.

If a STA in the RSB-PS mode does not have an AID (i.e., it released itsAID when entering the RSB-PS mode), it will have an AID assigned as partof its RSB-PS mode termination process or immediately following it. Inaddition, as part of the RSB-PS mode termination process, the systemparameters for system configurations, including security keys, may alsobe checked to confirm if the STA has the synchronized system settingswith the AP.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element may be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

What is claimed is:
 1. A method to provide access to a medium, themethod comprising: receiving a time value at a wireless station;receiving a traffic indication map (TIM) element at the wirelessstation, wherein the TIM element comprises bits mapped to an associationidentifier (AID) of the wireless station; on a condition that anindication for accessing a channel in a time interval for wirelessstations having AIDs associated with a positive indication in the TIMelement is received at the wireless station, determining a backoffnumber for the wireless station as a function of an index of the AID ofthe wireless station; on a condition that the indication is not receivedat the wireless station, determining the backoff number for the wirelessstation as a function of the AID of the wireless station; anddetermining a medium access backoff time for the wireless station bymultiplying the backoff number by the time value.
 2. The methodaccording to claim 1, wherein the time value is a fixed value.
 3. Themethod according to claim 1, wherein the time value is received at thewireless station via a beacon or a short beacon.
 4. The method accordingto claim 1, further comprising: setting a backoff timer at the wirelessstation with the medium access backoff time; and attempting to send acommunication by the wireless station after the backoff timer hasexpired.
 5. The method according to claim 1, wherein the medium accessbackoff time is a slot time.
 6. The method according to claim 1, furthercomprising signaling the medium access backoff time using at least oneof a beacon or a short beacon.
 7. The method according to claim 1,wherein the index is associated with the positive indication in the TIMelement.
 8. A wireless station, comprising: a transceiver configured toreceive a time value and a traffic indication map (TIM) element, whereinthe TIM element comprises bits mapped to an association identifier (AID)of the wireless station; and a processor in communication with thetransceiver, the processor configured to on a condition that anindication for accessing a channel in a time interval for wirelessstations having AIDs associated with a positive indication in the TIMelement is received at the wireless station, determine a backoff numberfor the wireless station as a function of an index of the AID of thewireless station; on a condition that the indication is not received atthe wireless station, determine the backoff number for the wirelessstation as a function of the AID of the wireless station; and determinea medium access backoff time for the wireless station by multiplying thebackoff number by the time value.
 9. The wireless station according toclaim 8, wherein the time value is a fixed value.
 10. The wirelessstation according to claim 8, wherein the transceiver is configured toreceive the time value via a beacon or a short beacon.
 11. The wirelessstation according to claim 8, further comprising: a backoff timer incommunication with the processor, the backoff timer being set to themedium access backoff time, wherein the transceiver attempts to send acommunication after the backoff timer has expired.
 12. The wirelessstation according to claim 8, wherein the medium access backoff time isa slot time.
 13. The wireless station according to claim 8, wherein thetransceiver is configured to signal the medium access backoff time usingat least one of a beacon or a short beacon.
 14. The wireless stationaccording to claim 8, wherein the index is associated with the positiveindication in the TIM element.